Fine powders for use in primary and secondary batteries

ABSTRACT

Fine battery powders and methods for producing fine battery powders. The powders have a well-controlled microstructure and morphology and preferably have a small average particle size. The method includes forming the particles from an aerosol of powder precursors. The invention also includes batteries formed from the powders.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fine powders useful for primary andsecondary batteries and to methods for producing such powders, as wellas products and devices incorporating the powders. The powders arepreferably produced by a spray conversion process.

2. Description of Related Art

Many primary (non-rechargeable and disposable) and secondary(rechargeable) batteries commonly utilize fine powders of an electrodematerial, such as LiCoO₂, LiNiO₂ and LiMn₂O₄. Such powders should haveone or more of the following properties: high purity; controlledcrystallinity; small average particle size; narrow particle sizedistribution; spherical particle morphology; controlled surfacechemistry; controlled surface area; and little or no agglomeration ofparticles.

With the advent of portable and hand-held electronic devices and anincreasing demand for electric automobiles due to the increased strainon natural resources there is a need for rapid development of highperformance, economical power systems. Such power systems requireimproved means for energy storage.

Electrodes used for such applications should have a high surface area toenhance the energy and power density capabilities of the battery. Forthese applications, powders of electrode component materials aredeposited over a large surface area and are typically impregnated withan electrode light.

To enhance the surface area it is desired that the powder componentmaterials be finally divided and of a relatively narrow particle sizedistribution. Porous particles are desirable because they provide alarge surface area to volume ratio. Similarly, wide distribution ofparticle sizes have a significant deleterious affect on energy densityof the cell. Agglomeration of the particles should also be avoided.

Finely divided powders have been difficult to obtain and to deposit withcontrol over layer thickness and uniformity. For preparation of powdersof cathode component materials conventional thermal processing followedby grinding and classification is commonly used. Even after heattreatment and grinding, the conversion may be substantially incompleteand the particle size of the product may be undesirable.

U.S. Pat. No. 5,648,057 by Ueda et al. discloses a method for producinglithium compounds in the form of powders that are useful for batteryelectrodes. The method includes the steps of reacting metal salts toform a slurry, drying the slurry and heating the resulting residue in anoxidative atmosphere.

U.S. Pat. No. 5,589,300 by Fauteux et al. discloses an aerosol processfor producing a precursor capable of being converted into a component ofan electrode, such as LiMn₂O₄.

The foregoing methods generally result in poor control over thecomposition and microstructure of the powders. The inability to controlthe fundamental powder characteristics is a major shortcoming for thefuture development and improvement of secondary and primary batteries.

It would be advantageous to provide a flexible production method capableof producing fine battery powders which would enable control over thepowder characteristics as well as the versatility to accommodatecompositions which are either difficult or impossible to produce usingexisting production methods. It would be advantageous to provide controlover the particle size, particle size distribution crystallinity,surface area of the powder, pore structure of the powder andcompositional uniformity. It would be particularly advantageous if suchpowders could be produced in large quantities on a substantiallycontinuous basis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process block diagram showing one embodiment of the processof the present invention.

FIG. 2 is a side view in cross section of one embodiment of aerosolgenerator of the present invention.

FIG. 3 is a top view of a transducer mounting plate showing a 49transducer array for use in an aerosol generator of the presentinvention.

FIG. 4 is a top view of a transducer mounting plate for a 400 transducerarray for use in an ultrasonic generator of the present invention.

FIG. 5 is a side view of the transducer mounting plate shown in FIG. 4.

FIG. 6 is a partial side view showing the profile of a single transducermounting receptacle of the transducer mounting plate shown in FIG. 4.

FIG. 7 is a partial side view in cross-section showing an alternativeembodiment for mounting an ultrasonic transducer.

FIG. 8 is a top view of a bottom retaining plate for retaining aseparator for use in an aerosol generator of the present invention.

FIG. 9 is a top view of a liquid feed box having a bottom retainingplate to assist in retaining a separator for use in an aerosol generatorof the present invention.

FIG. 10 is a side view of the liquid feed box shown in FIG. 9.

FIG. 11 is a side view of a gas tube for delivering gas within anaerosol generator of the present invention.

FIG. 12 shows a partial top view of gas tubes positioned in a liquidfeed box for distributing gas relative to ultrasonic transducerpositions for use in an aerosol generator of the present invention.

FIG. 13 shows one embodiment for a gas distribution configuration forthe aerosol generator of the present invention.

FIG. 14 shows another embodiment for a gas distribution configurationfor the aerosol generator of the present invention.

FIG. 15 is a top view of one embodiment of a gas distribution plate/gastube assembly of the aerosol generator of the present invention.

FIG. 16 is a side view of one embodiment of the gas distributionplate/gas tube assembly shown in FIG. 15.

FIG. 17 shows one embodiment for orienting a transducer in the aerosolgenerator of the present invention.

FIG. 18 is a top view of a gas manifold for distributing gas within anaerosol generator of the present invention.

FIG. 19 is a side view of the gas manifold shown in FIG. 18.

FIG. 20 is a top view of a generator lid of a hood design for use in anaerosol generator of the present invention.

FIG. 21 is a side view of the generator lid shown in FIG. 20.

FIG. 22 is a process block diagram of one embodiment of the process ofthe present invention including a droplet classifier.

FIG. 23 is a top view in cross section of an impactor of the presentinvention for use in classifying an aerosol.

FIG. 24 is a front view of a flow control plate of the impactor shown inFIG. 23.

FIG. 25 is a front view of a mounting plate of the impactor shown inFIG. 23.

FIG. 26 is a front view of an impactor plate assembly of the impactorshown in FIG. 23.

FIG. 27 is a side view of the impactor plate assembly shown in FIG. 26.

FIG. 28 is a process block diagram of one embodiment of the presentinvention including a particle cooler.

FIG. 29 is a top view of a gas quench cooler of the present invention.

FIG. 30 is an end view of the gas quench cooler shown in FIG. 29.

FIG. 31 is a side view of a perforated conduit of the quench coolershown in FIG. 29.

FIG. 32 is a side view showing one embodiment of a gas quench cooler ofthe present invention connected with a cyclone.

FIG. 33 is a process block diagram of one embodiment of the presentinvention including a particle coater.

FIG. 34 is a block diagram of one embodiment of the present inventionincluding a particle modifier.

FIG. 35 shows cross sections of various particle morphologies of somecomposite particles manufacturable according to the present invention.

FIG. 36 is a block diagram of one embodiment of the process of thepresent invention including the addition of a dry gas between theaerosol generator and the furnace.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is generally directed to fine battery powders andmethods for producing fine battery powders. The invention is alsodirected to novel devices fabricated using the powders. As used herein,fine battery powders or battery particles are those that are useful asan active component of an electrode in a primary or secondary battery.Specific examples of such powders are listed in more detail below.

In one aspect, the present invention provides a method for preparing aparticulate product including an active battery material. A feed ofliquid-containing, flowable medium, including at least one precursor forthe desired particulate product, is converted to aerosol form, withdroplets of the medium being dispersed in and suspended by a carriergas. Liquid from the droplets in the aerosol is then removed to permitformation in a dispersed state of the desired particles. In oneembodiment, the particles can be subjected, while still in a dispersedstate, to compositional or structural modification such ascrystallization, recrystallization or morphological alteration of theparticles. The term powder is often used herein to refer to theparticulate product of the present invention. The use of the term powderdoes not indicate, however, that the particulate product must be dry orin any particular environment. Although the particulate product istypically manufactured in a dry state, the particulate product may,after manufacture, be placed in a wet environment, such as in a paste orslurry.

The process of the present invention is particularly well suited for theproduction of finely divided particles having a small weight averagesize. In addition to making particles within a desired range of weightaverage particle size, the particles may advantageously be produced witha narrow size distribution, thereby providing size uniformity that isdesired for many applications. In addition, the method of the presentinvention provides significant flexibility for producing particles ofvarying composition, crystallinity, morphology and microstructure.

Referring now to FIG. 1, one embodiment of the process of the presentinvention is described. A liquid feed 102, including the precursor forthe desired particles, and a carrier gas 104 are fed to an aerosolgenerator 106 where an aerosol 108 is produced. The aerosol 108 is thenfed to a furnace 110 where liquid in the aerosol 108 is removed toproduce particles 112 that are dispersed in and suspended by gas exitingthe furnace 110. The particles 112 are then collected in a particlecollector 114 to produce a particulate product 116.

As used herein, the liquid feed 102 is a feed that includes one or moreflowable liquids as the major constituent(s), such that the feed is aflowable medium. The liquid feed 102 need not comprise only liquidconstituents. The liquid feed 102 may comprise only constituents in oneor more liquid phase, or it may also include particulate materialsuspended in a liquid phase. The liquid feed 102 must, however, becapable of being atomized to form droplets of sufficiently small sizefor preparation of the aerosol 108. Therefore, if the liquid feed 102includes suspended particles, those particles should be relatively smallin relation to the size of droplets in the aerosol 108. Such suspendedparticles should typically be not larger than about 1 μm in size,preferably not larger than about 0.5 μm in size, and more preferably notlarger than about 0.3 μm in size and most preferably not larger thanabout 0.1 μm in size. Most preferably, the suspended particles should becolloidal. The suspended particles could be finely divided particles, orcould be agglomerate masses comprised of agglomerated smaller primaryparticles. For example, 0.5 μm particles could be agglomerates ofnanometer-sized primary particles.

As noted, the liquid feed 102 includes one or more precursors forpreparation of the particles 112. The precursor may be a substance ineither a liquid or solid phase of the liquid feed 102. Frequently, theprecursor will be a material, such as a salt, dissolved in a liquidsolvent of the liquid feed 102. The precursor may undergo one or morechemical reactions in the furnace 110 to assist in production of theparticles 112. Alternatively, the precursor material may contribute toformation of the particles 112 without undergoing a substantial chemicalreaction. This could be the case, for example, when the liquid feed 102includes, as a precursor material, suspended particles that are notsubstantially chemically modified in the furnace 110. In any event, theparticles 112 comprise at least one component originally contributed bythe precursor.

For the production of fine battery powders, the liquid feed 102 willinclude multiple precursor materials, which may be present together in asingle phase or separately in multiple phases. For example, the liquidfeed 102 may include multiple precursors in solution in a single liquidvehicle. Also, one precursor material could be in one liquid phase and asecond precursor material could be in a second liquid phase, such ascould be the case when the liquid feed 102 comprises an emulsion.Examples of such precursor solutions and the reactions to form finebattery powders are detailed herein below:

The carrier gas 104 may comprise any gaseous medium in which dropletsproduced from the liquid feed 102 may be dispersed in aerosol form. Thecarrier gas 104 may be inert, in that the carrier gas 104 does notparticipate in formation of the particles 112. Alternatively, thecarrier gas may have one or more active component(s) that contribute toformation of the particles 112. In that regard, the carrier gas mayinclude one or more reactive components that react in the furnace 110 tocontribute to formation of the particles 112.

The aerosol generator 106 atomizes the liquid feed 102 to form dropletsin a manner to permit the carrier gas 104 to sweep the droplets away toform the aerosol 108. The droplets comprise liquid from the liquid feed102. The droplets may also include nonliquid material, such as one ormore small particles held in the droplet by the liquid. For example, onephase of the particles may be provided in the liquid feed 102 in theform of suspended precursor particles and a second phase of theparticles may be produced in the furnace 110 from one or more precursorsin the liquid phase of the liquid feed 102. Furthermore, the precursorparticles could be included in the liquid feed 102, and therefore alsoin droplets of the aerosol 108, for the purpose only of dispersing theparticles for subsequent compositional or structural modification duringor after processing in the furnace 110.

An important aspect of the present invention is generation of theaerosol 108 with droplets of a small average size and, preferably, anarrow size distribution. In this manner, the particles 112 may beproduced at a desired small size with a narrow size distribution, whichis advantageous for many applications.

The aerosol generator 106 is preferably capable of producing the aerosol108 such that it includes droplets having a weight average size in arange having a lower limit of about 1 μm and preferably about 2 μm; andan upper limit of about 20 μm; preferably about 10 μm, more preferablyabout 7 μm and most preferably about 5 μm. A weight average droplet sizein a range of from about 2 μm to about 4 μm is preferred for manyapplications. The aerosol generator is also capable of producing theaerosol 108 such that it includes droplets having a narrow sizedistribution. Preferably, the droplets in the aerosol are such that atleast about 70 percent (more preferably at least about 80 weight percentand most preferably at least about 85 weight percent) of the dropletsare smaller than about 10 μm and more preferably at least about 70weight percent (more preferably at least about 80 weight percent andmost preferably at least about 85 weight percent) are smaller than about5 μm. Furthermore, preferably no greater than about 30 weight percent,more preferably no greater than about 25 weight percent and mostpreferably no greater than about 20 weight percent, of the droplets inthe aerosol 108 are larger than about twice the weight average dropletsize.

Another important aspect of the present invention is that the aerosol108 may be generated without consuming excessive amounts of the carriergas 104. The aerosol generator 106 is capable of producing the aerosol108 such that it has a high loading, or high concentration, of theliquid feed 102 in droplet form. In that regard, the aerosol 108preferably includes greater than about 1×10⁶ droplets per cubiccentimeter of the aerosol 108, more preferably greater than about 5×10⁶droplets per cubic centimeter, still more preferably greater than about1×10⁷ droplets per cubic centimeter, and most preferably greater thanabout 5×10⁷ droplets per cubic centimeter. That the aerosol generator106 can produce such a heavily loaded aerosol 108 is particularlysurprising considering the high quality of the aerosol 108 with respectto small average droplet size and narrow droplet size distribution.Typically, droplet loading in the aerosol is such that the volumetricratio of liquid feed 102 to carrier gas 104 in the aerosol 108 is largerthan about 0.04 milliliters of liquid feed 102 per liter of carrier gas104 in the aerosol 108, preferably larger than about 0.083 millilitersof liquid feed 102 per liter of carrier gas 104 in the aerosol 108, morepreferably larger than about 0.167 milliliters of liquid feed 102 perliter of carrier gas 104, still more preferably larger than about 0.25milliliters of liquid feed 102 per liter of carrier gas 104, and mostpreferably larger than about 0.333 milliliters of liquid feed 102 perliter of carrier gas 104.

This capability of the aerosol generator 106 to produce a heavily loadedaerosol 108 is even more surprising given the high droplet output rateof which the aerosol generator 106 is capable, as discussed more fullybelow. It will be appreciated that the concentration of liquid feed 102in the aerosol 108 will depend upon the specific components andattributes of the liquid feed 102 and, particularly, the size of thedroplets in the aerosol 108.

For example, when the average droplet size is from about 2 μm to about 4μm, the droplet loading is preferably larger than about 0.15 millilitersof aerosol feed 102 per liter of carrier gas 104, more preferably largerthan about 0.2 milliliters of liquid feed 102 per liter of carrier gas104, even more preferably larger than about 0.25 milliliters of liquidfeed 102 per liter of carrier gas 104, and most preferably larger thanabout 0.3 milliliters of liquid feed 102 per liter of carrier gas 104.When reference is made herein to liters of carrier gas 104, it refers tothe volume that the carrier gas 104 would occupy under conditions ofstandard temperature and pressure.

The furnace 110 may be any suitable device for heating the aerosol 108to evaporate liquid from the droplets of the aerosol 108 and therebypermit formation of the particles 112. The maximum average streamtemperature, or reaction temperature, refers to the maximum averagetemperature that an aerosol stream attains while flowing through thefurnace. This is typically determined by a temperature probe insertedinto the furnace. Preferred reaction temperatures according to thepresent invention are discussed more fully below.

Although longer residence times are possible, for many applications,residence time in the heating zone of the furnace 110 of shorter thanabout 4 seconds is typical, such as from about 1 to 2 seconds. Theresidence time should be long enough, however, to assure that theparticles 112 attain the desired maximum stream temperature for a givenheat transfer rate. In that regard, with extremely short residencetimes, higher furnace temperatures could be used to increase the rate ofheat transfer so long as the particles 112 attain a maximum temperaturewithin the desired stream temperature range. That mode of operation,however, is not preferred. Also, it is preferred that, in most cases,the maximum stream temperature not be attained in the furnace 110 untilsubstantially at the end of the heating zone in the furnace 110. Forexample, the heating zone will often include a plurality of heatingsections that are each independently controllable. The maximum streamtemperature should typically not be attained until the final heatingsection, and more preferably until substantially at the end of the lastheating section. This is important to reduce the potential forthermophoretic losses of material. Also, it is noted that as usedherein, residence time refers to the actual time for a material to passthrough the relevant process equipment. In the case of the furnace, thisincludes the effect of increasing velocity with gas expansion due toheating.

Typically, the furnace 110 will be a tube-shaped furnace, so that theaerosol 108 moving into and through the furnace does not encounter sharpedges on which droplets could collect. Loss of droplets to collection atsharp surfaces results in a lower yield of particles 112. Further, theaccumulation of liquid at sharp edges can result in re-release ofundesirably large droplets back into the aerosol 108, which can causecontamination of the particulate product 116 with undesirably largeparticles. Also, over time, such liquid collection at sharp surfaces cancause fouling of process equipment, impairing process performance.

The furnace 110 may include a heating tube made of any suitablematerial. The tube material may be a ceramic material, for example,mullite, silica or alumina. Alternatively, the tube may be metallic.Advantages of using a metallic tube are low cost, ability to withstandsteep temperature gradients and large thermal shocks, machinability andweldability, and ease of providing a seal between the tube and otherprocess equipment. Disadvantages of using a metallic tube includelimited operating temperature and increased reactivity in some reactionsystems.

When a metallic tube is used in the furnace 110, it is preferably a highnickel content stainless steel alloy, such as a 330 stainless steel, ora nickel-based super alloy. As noted, one of the major advantages ofusing a metallic tube is that the tube is relatively easy to seal withother process equipment. In that regard, flange fittings may be weldeddirectly to the tube for connecting with other process equipment.Metallic tubes are generally preferred for making particles that do notrequire a maximum tube wall temperature of higher than about 1100° C.during particle manufacture.

When higher temperatures are required, ceramic tubes are typically used.One major problem with ceramic tubes, however, is that the tubes can bedifficult to seal with other process equipment, especially when the endsof the tubes are maintained at relatively high temperatures, as is oftenthe case with the present invention.

Also, although the present invention is described with primary referenceto a furnace reactor, which is preferred, it should be recognized that,except as noted, any other thermal reactor, including a flame reactor ora plasma reactor, could be used instead. A furnace reactor is, however,preferred, because of the generally even heating characteristic of afurnace for attaining a uniform stream temperature.

The particle collector 114, may be any suitable apparatus for collectingparticles 112 to produce the particulate product 116. One preferredembodiment of the particle collector 114 uses one or more filter toseparate the particles 112 from the gas, Such a filter may be of anytype, including a bag filter. Another preferred embodiment of theparticle collector uses one or more cyclone to separate the particles112. Other apparatus that may be used in the particle collector 114includes an electrostatic precipitator. Also, collection should normallyoccur at a temperature above the condensation temperature of the gasstream in which the particles 112 are suspended. Further, collectionshould normally be at a temperature that is low enough to preventsignificant agglomeration of the particles 112.

Of significant importance to the operation of the process of the presentinvention is the aerosol generator 106, which must be capable ofproducing a high quality aerosol with high droplet loading, aspreviously noted. With reference to FIG. 2, one embodiment of an aerosolgenerator 106 of the present invention is described. The aerosolgenerator 106 includes a plurality of ultrasonic transducer discs 120that are each mounted in a transducer housing 122. The transducerhousings 122 are mounted to a transducer mounting plate 124, creating anarray of the ultrasonic transducer discs 120. Any convenient spacing maybe used for the ultrasonic transducer discs 120. Center-to-centerspacing of the ultrasonic transducer discs 120 of about 4 centimeters isoften adequate. The aerosol generator 106, as shown in FIG. 2, includesforty-nine transducers in a 7×7 array. The array configuration is asshown in FIG. 3, which depicts the locations of the transducer housings122 mounted to the transducer mounting plate 124.

With continued reference to FIG. 2, a separator 126, in spaced relationto the transducer discs 120, is retained between a bottom retainingplate 128 and a top retaining plate 130. Gas delivery tubes 132 areconnected to gas distribution manifolds 134, which have gas deliveryports 136. The gas distribution manifolds 134 are housed within agenerator body 138 that is covered by generator lid 140. A transducerdriver 144, having circuitry for driving the transducer discs 120, iselectronically connected with the transducer discs 120 via electricalcables 146.

During operation of the aerosol generator 106, as shown in FIG. 2, thetransducer discs 120 are activated by the transducer driver 144 via theelectrical cables 146. The transducers preferably vibrate at a frequencyof from about 1 MHz to about 5 MHz, more preferably from about 1.5 MHzto about 3 MHz. Commonly used frequencies are at about 1.6 MHz and about2.4 MHz. Furthermore, all of the transducer discs 110 should beoperating at substantially the same frequency when an aerosol with anarrow droplet size distribution is desired. This is important becausecommercially available transducers can vary significantly in thickness,sometimes by as much as 10%. It is preferred, however, that thetransducer discs 120 operate at frequencies within a range of 5% aboveand below the median transducer frequency, more preferably within arange of 2.5%, and most preferably within a range of 1%. This can beaccomplished by careful Selection of the transducer discs 120 so thatthey all preferably have thicknesses within 5% of the median transducerthickness, more preferably within 2.5%, and most preferably within 1%.

Liquid feed 102 enters through a feed inlet 148 and flows through flowchannels 150 to exit through feed outlet 152. An ultrasonicallytransmissive fluid, typically water, enters through a water inlet 154 tofill a water bath volume 156 and flow through flow channels 158 to exitthrough a water outlet 160. A proper flow rate of the ultrasonicallytransmissive fluid is necessary to cool the transducer discs 120 and toprevent overheating of the ultrasonically transmissive fluid. Ultrasonicsignals from the transducer discs 120 are transmitted, via theultrasonically transmissive fluid, across the water bath volume 156, andultimately across the separator 126, to the liquid feed 102 in flowchannels 150.

The ultrasonic signals from the ultrasonic transducer discs 120 causeatomization cones 162 to develop in the liquid feed 102 at locationscorresponding with the transducer discs 120. Carrier gas 104 isintroduced into the gas delivery tubes 132 and delivered to the vicinityof the atomization cones 162 via gas delivery ports 136. Jets of carriergas exit the gas delivery ports 136 in a direction so as to impinge onthe atomization cones 162, thereby sweeping away atomized droplets ofthe liquid feed 102 that are being generated from the atomization cones162 and creating the aerosol 108, which exits the aerosol generator 106through an aerosol exit opening 164.

Efficient use of the carrier gas 104 is an important aspect of theaerosol generator 106. The embodiment of the aerosol generator 106 shownin FIG. 2 includes two gas exit ports per atomization cone 162, with thegas ports being positioned above the liquid medium 102 over troughs thatdevelop between the atomization cones 162, such that the exiting carriergas 104 is horizontally directed at the surface of the atomization cones162, thereby efficiently distributing the carrier gas 104 to criticalportions of the liquid feed 102 for effective and efficient sweepingaway of droplets as they form about the ultrasonically energizedatomization cones 162. Furthermore, it is preferred that at least aportion of the opening of each of the gas delivery ports 136, throughwhich the carrier gas exits the gas delivery tubes, should be locatedbelow the top of the atomization cones 162 at which the carrier gas 104is directed. This relative placement of the gas delivery ports 136 isvery important to efficient use of carrier gas 104. Orientation of thegas delivery ports 136 is also important. Preferably, the gas deliveryports 136 are positioned to horizontally direct jets of the carrier gas104 at the atomization cones 162. The aerosol generator 106 permitsgeneration of the aerosol 108 with heavy loading with droplets of thecarrier liquid 102, unlike aerosol generator designs that do notefficiently focus gas delivery to the locations of droplet formation.

Another important feature of the aerosol generator 106, as shown in FIG.2, is the use of the separator 126, which protects the transducer discs120 from direct contact with the liquid feed 102, which is often highlycorrosive. The height of the separator 126 above the top of thetransducer discs 120 should normally be kept as small as possible, andis often in the range of from about 1 centimeter to about 2 centimeters.The top of the liquid feed 102 in the flow channels above the tops ofthe ultrasonic transducer discs 120 is typically in a range of fromabout 2 centimeters to about 5 centimeters, whether or not the aerosolgenerator includes the separator 126, with a distance of about 3 to 4centimeters being preferred. Although the aerosol generator 106 could bemade without the separator 126, in which case the liquid feed 102 wouldbe in direct contact with the transducer discs 120, the highly corrosivenature of the liquid feed 102 can often cause premature failure of thetransducer discs 120. The use of the separator 126, in combination withuse of the ultrasonically transmissive fluid in the water bath volume156 to provide ultrasonic coupling, significantly extends the life ofthe ultrasonic transducers 120. One disadvantage of using the separator126, however, is that the rate of droplet production from theatomization cones 162 is reduced, often by a factor of two or more,relative to designs in which the liquid feed 102 is in direct contactwith the ultrasonic transducer discs 102. Even with the separator 126,however, the aerosol generator 106 used with the present invention iscapable of producing a high quality aerosol with heavy droplet loading,as previously discussed. Suitable materials for the separator 126include, for example, polyamides (such as Kapton™ membranes from DuPont)and other polymer materials, glass, and plexiglass. The mainrequirements for the separator 126 are that it be ultrasonicallytransmissive, corrosion resistant and impermeable.

One alternative to using the separator 126 is to bind acorrosion-resistant protective coating onto the surface of theultrasonic transducer discs 120, thereby preventing the liquid feed 102from contacting the surface of the ultrasonic transducer discs 120. Whenthe ultrasonic transducer discs 120 have a protective coating, theaerosol generator 106 will typically be constructed without the waterbath volume 156 and the liquid feed 102 will flow directly over theultrasonic transducer discs 120. Examples of such protective coatingmaterials include platinum, gold, TEFLON™, epoxies and various plastics.Such coating typically significantly extends transducer life. Also, whenoperating without the separator 126, the aerosol generator 106 willtypically produce the aerosol 108 with a much higher droplet loadingthan when the separator 126 is used.

One surprising finding with operation of the aerosol generator 106 ofthe present invention is that the droplet loading in the aerosol may beaffected by the temperature of the liquid feed 102. It has been foundthat when the liquid feed 102 includes an aqueous liquid at an elevatedtemperature, the droplet loading increases significantly. Thetemperature of the liquid feed 102 is preferably higher than about 30°C., more preferably higher than about 35° C. and most preferably higherthan about 40° C. If the temperature becomes too high, however, it canhave a detrimental effect on droplet loading in the aerosol 108.Therefore, the temperature of the liquid feed 102 from which the aerosol108 is made should generally be lower than about 50° C., and preferablylower than about 45° C. The liquid feed 102 may be maintained at thedesired temperature in any suitable fashion. For example, the portion ofthe aerosol generator 106 where the liquid feed 102 is converted to theaerosol 108 could be maintained at a constant elevated temperature.Alternatively, the liquid feed 102 could be delivered to the aerosolgenerator 106 from a constant temperature bath maintained separate fromthe aerosol generator 106. When the ultrasonic generator 106 includesthe separator 126, the ultrasonically transmissive fluid adjacent theultrasonic transducer discs 120 are preferably also at an elevatedtemperature in the ranges discussed for the liquid feed 102.

The design for the aerosol generator 106 based on an array of ultrasonictransducers is versatile and is easily modified to accommodate differentgenerator sizes for different specialty applications. The aerosolgenerator 106 may be designed to include a plurality of ultrasonictransducers in any convenient number. Even for smaller scale production,however, the aerosol generator 106 preferably has at least nineultrasonic transducers, more preferably at least 16 ultrasonictransducers, and even more preferably at least 25 ultrasonictransducers. For larger scale production, however, the aerosol generator106 includes at least 40 ultrasonic transducers, more preferably atleast 100 ultrasonic transducers, and even more preferably at least 400ultrasonic transducers. In some large volume applications, the aerosolgenerator may have at least 1000 ultrasonic transducers.

FIGS. 4-21 show component designs for an aerosol-generator 106 includingan array of 400 ultrasonic transducers. Referring first to FIGS. 4 and5, the transducer mounting plate 124 is shown with a design toaccommodate an array of 400 ultrasonic transducers, arranged in foursubarrays of 100 ultrasonic transducers each. The transducer mountingplate 124 has integral vertical walls 172 for containing theultrasonically transmissive fluid, typically water, in a water bathsimilar to the water bath volume 156 described previously with referenceto FIG. 2.

As shown in FIGS. 4 and 5, four hundred transducer mounting receptacles174 are provided in the transducer mounting plate 124 for mountingultrasonic transducers for the desired array. With reference to FIG. 6,the profile of an individual transducer mounting receptacle 174 isshown. A mounting seat 176 accepts an ultrasonic transducer formounting, with a mounted ultrasonic transducer being held in place viascrew holes 178. Opposite the mounting receptacle 176 is a flaredopening 180 through which an ultrasonic signal may be transmitted forthe purpose of generating the aerosol 108, as previously described withreference to FIG. 2.

A preferred transducer mounting configuration, however, is shown in FIG.7 for another configuration for the transducer mounting plate 124. Asillustrated in FIG. 7, an ultrasonic transducer disc 120 is mounted tothe transducer mounting plate 124 by use of a compression screw 177threaded into a threaded receptacle 179. The compression screw 177 bearsagainst the ultrasonic transducer disc 120, causing an o-ring 181,situated in an o-ring seat 182 on the transducer mounting plate, to becompressed to form a seal between the transducer mounting plate 124 andthe ultrasonic transducer disc 120. This type of transducer mounting isparticularly preferred when the ultrasonic transducer disc 120 includesa protective surface coating, as discussed previously, because the sealof the o-ring to the ultrasonic transducer disc 120 will be inside ofthe outer edge of the protective seal, thereby preventing liquid frompenetrating under the protective surface coating from the edges of theultrasonic transducer disc 120.

Referring now to FIG. 8, the bottom retaining plate 128 for a 400transducer array is shown having a design for mating with the transducermounting plate 124 (shown in FIGS. 4-5). The bottom retaining plate 128has eighty openings 184, arranged in four subgroups 186 of twentyopenings 184 each. Each of the openings 184 corresponds with five of thetransducer mounting receptacles 174 (shown in FIGS. 4 and 5) when thebottom retaining plate 128 is mated with the transducer mounting plate124 to create a volume for a water bath between the transducer mountingplate 124 and the bottom retaining plate 128. The openings 184,therefore, provide a pathway for ultrasonic signals generated byultrasonic transducers to be transmitted through the bottom retainingplate.

Referring now to FIGS. 9 and 10, a liquid feed box 190 for a 400transducer array is shown having the top retaining plate 130 designed tofit over the bottom retaining plate 128 (shown in FIG. 8), with aseparator 126 (not shown) being retained between the bottom retainingplate 128 and the top retaining plate 130 when the aerosol generator 106is assembled. The liquid feed box 190 also includes vertically extendingwalls 192 for containing the liquid feed 102 when the aerosol generatoris in operation. Also shown in FIGS. 9 and 10 is the feed inlet 148 andthe feed outlet 152. An adjustable weir 198 determines the level ofliquid feed 102 in the liquid feed box 190 during operation of theaerosol generator 106.

The top retaining plate 130 of the liquid feed box 190 has eightyopenings 194 therethrough, which are arranged in four subgroups 196 oftwenty openings 194 each. The openings 194 of the top retaining plate130 correspond in size with the openings 184 of the bottom retainingplate 128 (shown in FIG. 8). When the aerosol generator 106 isassembled, the openings 194 through the top retaining plate 130 and theopenings 184 through the bottom retaining plate 128 are aligned, withthe separator 126 positioned therebetween, to permit transmission ofultrasonic signals when the aerosol generator 106 is in operation.

Referring now to FIGS. 9-11, a plurality of gas tube feed-through holes202 extend through the vertically extending walls 192 to either side ofthe assembly including the feed inlet 148 and feed outlet 152 of theliquid feed box 190. The gas tube feed-through holes 202 are designed topermit insertion therethrough of gas tubes 208 of a design as shown inFIG. 11. When the aerosol generator 106 is assembled, a gas tube 208 isinserted through each of the gas tube feed-through holes 202 so that gasdelivery ports 136 in the gas tube 208 will be properly positioned andaligned adjacent the openings 194 in the top retaining plate 130 fordelivery of gas to atomization cones that develop in the liquid feed box190 during operation of the aerosol generator 106. The gas deliveryports 136 are typically holes having a diameter of from about 1.5millimeters to about 3.5 millimeters.

Referring now to FIG. 12, a partial view of the liquid feed box 190 isshown with gas tubes 208A, 208B and 208C positioned adjacent to theopenings 194 through the top retaining plate 130. Also shown in FIG. 12are the relative locations that ultrasonic transducer discs 120 wouldoccupy when the aerosol generator 106 is assembled. As seen in FIG. 15,the gas tube 208A, which is at the edge of the array, has five gasdelivery ports 136. Each of the gas delivery ports 136 is positioned todivert carrier gas 104 to a different one of atomization cones thatdevelop over the array of ultrasonic transducer discs 120 when theaerosol generator 106 is operating. The gas tube 208B, which is one rowin from the edge of the array, is a shorter tube that has ten gasdelivery ports 136, five each on opposing sides of the gas tube 208B.The gas tube 208B, therefore, has gas delivery ports 136 for deliveringgas to atomization cones corresponding with each of ten ultrasonictransducer discs 120. The third gas tube, 208C, is a longer tube thatalso has ten gas delivery ports 136 for delivering gas to atomizationcones corresponding with ten ultrasonic transducer discs 120. The designshown in FIG. 12, therefore, includes one gas delivery port perultrasonic transducer disc 120. Although this is a lower density of gasdelivery ports 136 than for the embodiment of the aerosol generator 106shown in FIG. 2, which includes two gas delivery ports per ultrasonictransducer disc 120, the design shown in FIG. 12 is, nevertheless,capable of producing a dense, high-quality aerosol without unnecessarywaste of gas.

Referring now to FIG. 13, the flow of carrier gas 104 relative toatomization cones 162 during operation of the aerosol generator 106having a gas distribution configuration to deliver carrier gas 104 fromgas delivery ports on both sides of the gas tubes 208, as was shown forthe gas tubes 208A, 208B and 208C in the gas distribution configurationshown in FIG. 11. The carrier gas 104 sweeps both directions from eachof the gas tubes 208.

An alternative, and preferred, flow for carrier gas 104 is shown in FIG.14. As shown in FIG. 14, carrier gas 104 is delivered from only one sideof each of the gas tubes 208. This results in a sweep of carrier gasfrom all of the gas-tubes 208 toward a central area 212. This results ina more uniform flow pattern for aerosol generation that maysignificantly enhance the efficiency with which the carrier gas 104 isused to produce an aerosol. The aerosol that is generated, therefore,tends to be more heavily loaded with liquid droplets.

Another configuration for distributing carrier gas in the aerosolgenerator 106 is shown in FIGS. 15 and 16. In this configuration, thegas tubes 208 are hung from a gas distribution plate 216 adjacent gasflow holes 218 through the gas distribution plate 216. In the aerosolgenerator 106, the gas distribution plate 216 would be mounted above theliquid feed, with the gas flow holes positioned to each correspond withan underlying ultrasonic transducer. Referring specifically to FIG. 16,when the ultrasonic generator 106 is in operation, atomization cones 162develop through the gas flow holes 218, and the gas tubes 208 arelocated such that carrier gas 104′ exiting from ports in the gas tubes208 impinge on the atomization cones and flow upward through the gasflow holes. The gas flow holes 218, therefore, act to assist inefficiently distributing the carrier gas 104 about the atomization cones162 for aerosol formation. It should be appreciated that the gasdistribution plates 218 can be made to accommodate any number of the gastubes 208 and gas flow holes 218. For convenience of illustration, theembodiment shown in FIGS. 15 and 16 shows a design having only two ofthe gas tubes 208 and only 16 of the gas flow holes 218. Also, it shouldbe appreciated that the gas distribution plate 216 could be used alone,without the gas tubes 208. In that case, a slight positive pressure ofcarrier gas 104 would be maintained under the gas distribution plate 216and the gas flow holes 218 would be sized to maintain the propervelocity of carrier gas 104 through the gas flow holes 218 for efficientaerosol generation. Because of the relative complexity of operating inthat mode, however, it is not preferred.

Aerosol generation may also be enhanced through mounting of ultrasonictransducers at a slight angle and directing the carrier gas at resultingatomization cones such that the atomization cones are tilting in thesame direction as the direction of flow of carrier gas. Referring toFIG. 17, an ultrasonic transducer disc 120 is shown. The ultrasonictransducer disc 120 is tilted at a tilt angle 114 (typically less than10 degrees), so that the atomization cone 162 will also have a tilt. Itis preferred that the direction of flow of the carrier gas 104 directedat the atomization cone 162 is in the same direction as the tilt of theatomization cone 162.

Referring now to FIGS. 18 and 19, a gas manifold 220 is shown fordistributing gas to the gas tubes 208 in a 400 transducer array design.The gas manifold 220 includes a gas distribution box 222 and pipingstubs 224 for connection with gas tubes 208 (shown in FIG. 11). Insidethe gas distribution box 222 are two gas distribution plates 226 thatform a flow path to assist in distributing the gas equally throughoutthe gas distribution box 222, to promote substantially equaL delivery ofgas through the piping stubs 224. The gas manifold 220, as shown inFIGS. 18 and 19, is designed to feed eleven gas tubes 208. For the 400transducer design, a total of four gas manifolds 220 are required.

Referring now to FIGS. 20 and 21, the generator lid 140 is shown for a400 transducer array design. The generator lid 140 mates with and coversthe liquid feed box 190 (shown in FIGS. 9 and 10). The generator lid140, as shown in FIGS. 20 and 21, has a hood design to permit easycollection of the aerosol 108 without subjecting droplets in the aerosol108 to sharp edges on which droplets may coalesce and be lost, andpossibly interfere with the proper operation of the aerosol generator106. When the aerosol generator 106 is in operation, the aerosol 108would be withdrawn via the aerosol exit opening 164 through thegenerator cover 140.

It is important that the aerosol stream fed to the furnace 110 have ahigh droplet flow rate and high droplet loading as would be required formost industrial applications. With the present invention, the aerosolstream fed to the furnace preferably includes a droplet flow of greaterthan about 0.5 liters per hour, more preferably greater than about 2liters per hour, still more preferably greater than about 5 liters perhour, even more preferably greater than about 10 liters per hour,particularly greater than about 50 liters per hour and most preferablygreater than about 100 liters per hour; and with the droplet loadingbeing typically greater than about 0.04 milliliters of droplets perliter of carrier gas, preferably greater than about 0.083 milliliters ofdroplets per liter of carrier gas 104, more preferably greater thanabout 0.167 milliliters of droplets per liter of carrier gas 104, stillmore preferably greater than about 0.25 milliliters of droplets perliter of carrier gas 104, particularly greater than about 0.33milliliters of droplets per liter of carrier gas 104 and most preferablygreater than about 0.83 milliliters of droplets per liter of carrier gas104.

As discussed previously, the aerosol generator 106 of the presentinvention produces a concentrated, high quality aerosol of micro-sizeddroplets having a relatively narrow size distribution. It has beenfound, however, that for many applications the process of the presentinvention is significantly enhanced by further classifying by size thedroplets in the aerosol 108 prior to introduction of the droplets intothe furnace 110. In this manner, the size and size distribution ofparticles in the particulate product 116 are further controlled.

Referring now to FIG. 22, a process flow diagram is shown for oneembodiment of the process of the present invention including suchdroplet classification. As shown in FIG. 22, the aerosol 108 from theaerosol generator 106 goes to a droplet classifier 280 where oversizeddroplets are removed from the aerosol 108 to prepare a classifiedaerosol 282. Liquid 284 from the oversized droplets that are beingremoved is drained from the droplet classifier 280. This drained liquid284 may advantageously be recycled for use in preparing additionalliquid feed 102.

Any suitable droplet classifier may be used for removing droplets abovea predetermined size. For example, a cyclone could be used to removeover-size droplets. A preferred droplet classifier for manyapplications, however, is an impactor. One embodiment of an impactor foruse with the present invention will now be described with reference toFIGS. 23-27.

As seen in FIG. 23, an impactor 288 has disposed in a flow conduit 286 aflow control plate 290 and an impactor plate assembly 292. The flowcontrol plate 290 is conveniently mounted on a mounting plate 294.

The flow control plate 290 is used to channel the flow of the aerosolstream toward the impactor plate assembly 292 in a manner withcontrolled flow characteristics that are desirable for proper impactionof oversize droplets on the impactor plate assembly 292 for removalthrough the drains 296 and 314. One embodiment of the flow control plate290 is shown in FIG. 24. The flow control plate 290 has an array ofcircular flow ports 296 for channeling flow of the aerosol 108 towardsthe impactor plate assembly 292 with the desired flow characteristics.

Details of the mounting plate 294 are shown in FIG. 25. The mountingplate 294 has mounting flange 298 with a large diameter flow opening 300passing therethrough to permit access of the aerosol 108 to the flowports 296 of the flow control plate 290 (shown in FIG. 24).

Referring now to FIGS. 26 and 27, one embodiment of an impactor plateassembly 292 is shown. The impactor plate assembly 292 includes animpactor plate 302 and mounting brackets 304 and 306 used to mount theimpactor plate 302 inside of the flow conduit 286. The impactor plate302 and the flow channel plate 290 are designed so that droplets largerthan a predetermined size will have momentum that is too large for thoseparticles to change flow direction to navigate around the impactor plate302.

During operation of the impactor 288, the aerosol 108 from the aerosolgenerator 106 passes through the upstream flow control plate 290. Mostof the droplets in the aerosol navigate around the impactor plate 302and exit the impactor 288 through the downstream flow control plate 290in the classified aerosol 282. Droplets in the aerosol 108 that are toolarge to navigate around the impactor plate 302 will impact on theimpactor plate 302 and drain through the drain 296 to be collected withthe drained liquid 284 (as shown in FIG. 23).

The configuration of the impactor plate 302 shown in FIG. 22 representsonly one of many possible configurations for the impactor plate 302. Forexample, the impactor 288 could include an upstream flow control plate290 having vertically extending flow slits therethrough that are offsetfrom vertically extending flow slits through the impactor plate 302,such that droplets too large to navigate the change in flow due to theoffset of the flow slits between the flow control plate 290 and theimpactor plate 302 would impact on the impactor plate 302 to be drainedaway. Other designs are also possible.

In a preferred embodiment of the present invention, the dropletclassifier 280 is typically designed to remove droplets from the aerosol108 that are larger than about 15 μm, more preferably to remove dropletslarger than about 10 μm, even more preferably to remove droplets of asize larger than about 8 μm and most preferably to remove dropletslarger than about 5 μm. The droplet classification size in the dropletclassifier is preferably smaller than about 15 μm, more preferablysmaller than about 10 μm, even more preferably smaller than about 8 μmand most preferably smaller than about 5 μm. The classification size,also called the classification cut point, is that size at which half ofthe droplets of that size are removed and half of the droplets of thatsize are retained. Depending upon the specific application, however, thedroplet classification size may be varied, such as by changing thespacing between the impactor plate 302 and the flow control plate 290 orincreasing or decreasing aerosol velocity through the jets in the flowcontrol plate 290. Because the aerosol generator 106 of the presentinvention initially produces a high quality aerosol 108, having arelatively narrow size distribution of droplets, typically less thanabout 30 weight percent of liquid feed 102 in the aerosol 108 is removedas the drain liquid 284 in the droplet classifier 288, with preferablyless than about 25 weight percent being removed, even more preferablyless than about 20 weight percent being removed and most preferably lessthan about 15 weight percent being removed. Minimizing the removal ofliquid feed 102 from the aerosol 108 is particularly important forcommercial applications to increase the yield of high qualityparticulate product 116. It should be noted, however, that because ofthe superior performance of the aerosol generator 106, it is typicallynot required to use an impactor or other droplet classifier to obtain asuitable aerosol. This is a major advantage, because the addedcomplexity and liquid losses accompanying use of an impactor may oftenbe avoided with the process of the present invention.

With some applications of the process of the present invention, it maybe possible to collect the particles 112 directly from the output of thefurnace 110. More often, however, it will be desirable to cool theparticles 112 exiting the furnace 110 prior to collection of theparticles 112 in the particle collector 114. Referring now to FIG. 28,one embodiment of the process of the present invention is shown in whichthe particles 112 exiting the furnace 110 are sent to a particle cooler320 to produce a cooled particle stream 322, which is then fed to theparticle collector 114. Although the particle cooler 320 may be anycooling apparatus capable of cooling the particles 112 to the desiredtemperature for introduction into the particle collector 114,traditional heat exchanger designs are not preferred. This is because atraditional heat exchanger design ordinarily directly subjects theaerosol stream, in which the hot particles 112 are suspended, to coolsurfaces. In that situation, significant losses of the particles 112occur due to thermophoretic deposition of the hot particles 112 on thecool surfaces of the heat exchanger. According to the present invention,a gas quench apparatus is provided for use as the particle cooler 320that significantly reduces thermophoretic losses compared to atraditional heat exchanger.

Referring now to FIGS. 29-31, one embodiment of a gas quench cooler 330is shown. The gas quench cooler includes a perforated conduit 332 housedinside of a cooler housing 334 with an annular space 336 located betweenthe cooler housing 334 and the perforated conduit 332. In fluidcommunication with the annular space 336 is a quench gas inlet box 338,inside of which is disposed a portion of an aerosol outlet conduit 340.The perforated conduit 332 extends between the aerosol outlet conduit340 and an aerosol inlet conduit 342. Attached to an opening into thequench gas inlet box 338 are two quench gas feed tubes 344. Referringspecifically to FIG. 31, the perforated tube 332 is shown. Theperforated tube 332 has a plurality of openings 345. The openings 345,when the perforated conduit 332 is assembled into the gas quench cooler330, permit the flow of quench gas 346 from the annular space 336 intothe interior space 348 of the perforated conduit 332. Although theopenings 345 are shown as being round holes, any shape of opening couldbe used, such as slits. Also, the perforated conduit 332 could be aporous screen. Two heat radiation shields 347 prevent downstream radiantheating from the furnace. In most instances, however, it will not benecessary to include the heat radiation shields 347, because downstreamradiant heating from the furnace is normally not a significant problem.Use of the heat radiation shields 347 is not preferred due toparticulate losses that accompany their use.

With continued reference to FIGS. 29-31, operation of the gas quenchcooler 330 will now be described. During operation, the particles 112,carried by and dispersed in a gas stream, enter the gas quench cooler330 through the aerosol inlet conduit 342 and flow into the interiorspace 348 of perforated conduit 332. Quench gas 346 is introducedthrough the quench gas feed tubes 344 into the quench gas inlet box 338.Quench gas 346 entering the quench gas inlet box 338 encounters theouter surface of the aerosol outlet conduit 340, forcing the quench gas346 to flow, in a spiraling, swirling manner, into the annular space336, where the quench gas 346 flows through the openings 345 through thewalls of the perforated conduit 332. Preferably, the gas 346 retainssome swirling motion even after passing into the interior space 348. Inthis way, the particles 112 are quickly cooled with low losses ofparticles to the walls of the gas quench cooler 330. In this manner, thequench gas 346 enters in a radial direction into the interior space 348of the perforated conduit 332 around the entire periphery, orcircumference, of the perforated conduit 332 and over the entire lengthof the perforated conduit 332. The cool quench gas 346 mixes with andcools the hot particles 112, which then exit through the aerosol outletconduit 340 as the cooled particle stream 322. The cooled particlestream 322 can then be sent to the particle collector 114 for particlecollection. The temperature of the cooled particle stream 322 iscontrolled by introducing more or less quench gas. Also, as shown inFIG. 32, the quench gas 346 is fed into the quench cooler 330 in counterflow to the flow of the particles. Alternatively, the quench coolercould be designed so that the quench gas 346 is fed into the quenchcooler in concurrent flow with the flow of the particles 112. The amountof quench gas 346 fed to the gas quench cooler 330 will depend upon thespecific material being made and the specific operating conditions. Thequantity of quench gas 346 used, however, must be sufficient to reducethe temperature of the aerosol steam including the particles 112 to thedesired temperature. Typically, the particles 112 are cooled to atemperature at least below about 200° C., and often lower. The onlylimitation on how much the particles 112 are cooled is that the cooledparticle stream 322 must be at a temperature that is above thecondensation temperature for water as another condensible vapor in thestream. The temperature of the cooled particle stream 322 is often at atemperature of from about 50° C. to about 120° C.

Because of the entry of quench gas 346 into the interior space 348 ofthe perforated conduit 322 in a radial direction about the entirecircumference and length of the perforated conduit 322, a buffer of thecool quench gas 346 is formed about the inner wall of the perforatedconduit 332, thereby significantly inhibiting the loss of hot particles112 due to thermophoretic deposition on the cool wall of the perforatedconduit 332. In operation, the quench gas 346 exiting the openings 345and entering into the interior space 348 should have a radial velocity(velocity inward toward the center of the circular cross-section of theperforated conduit 332) of larger than the thermophoretic velocity ofthe particles 112 inside the perforated conduit 332 in a directionradially outward toward the perforated wall of the perforated conduit332.

As seen in FIGS. 29-31, the gas quench cooler 330 includes a flow pathfor the particles 112 through the gas quench cooler of a substantiallyconstant cross-sectional shape and area. Preferably, the flow paththrough the gas quench cooler 330 will have the same cross-sectionalshape and area as the flow path through the furnace 110 and through theconduit delivering the aerosol 108 from the aerosol generator 106 to thefurnace 110. In one embodiment, however, it may be necessary to reducethe cross-sectional area available for flow prior to the particlecollector 114. This is the case, for example, when the particlecollector includes a cyclone for separating particles in the cooledparticle stream 322 from gas in the cooled particle stream 322. This isbecause of the high inlet velocity requirements into cyclone separators.

Referring now to FIG. 32, one embodiment of the gas quench cooler 330 isshown in combination with a cyclone separator 392. The perforatedconduit 332 has a continuously decreasing cross-sectional area for flowto increase the velocity of flow to the proper value for the feed tocyclone separator 392. Attached to the cyclone separator 392 is a bagfilter 394 for final clean-up of overflow from the cyclone separator392. Separated particles exit with underflow from the cyclone separator392 and may be collected in any convenient container. The use of cycloneseparation is particularly preferred for powder having a weight averagesize of larger than about 1 μm, although a series of cyclones maysometimes be needed to obtain the desired degree of separation. Cycloneseparation is particularly preferred for powders having a weight averagesize of larger than about 1.5 μm.

In an additional embodiment, the process of the present invention canalso incorporate compositional modification of the particles 112 exitingthe furnace. Most commonly, the compositional modification will involveforming on the particles 112 a material phase that is different thanthat of the particles 112, such as by coating the particles 112 with acoating material. One embodiment of the process of the present inventionincorporating particle coating is shown in FIG. 33. As shown in FIG. 33,the particles 112 exiting from the furnace 110 go to a particle coater350 where a coating is placed over the outer surface of the particles112 to form coated particles 352, which are then sent to the particlecollector 114 for preparation of the particulate product 116.

With continued reference primarily to FIG. 33, in a preferredembodiment, when the particles 112 are coated according to the processof the present invention, the particles 112 are also manufactured viathe aerosol process of the present invention, as previously described.The process of the present invention can, however, be used to coatparticles that have been premanufactured by a different process. Whencoating particles that have been premanufactured by a different route,such as by liquid precipitation, it is preferred that the particlesremain in a dispersed state from the time of manufacture to the timethat the particles are introduced in slurry form into the aerosolgenerator 106 for preparation of the aerosol 108 to form the dryparticles 112 in the furnace 110, which particles 112 can then be coatedin the particle coater 350. Maintaining particles in a dispersed statefrom manufacture through coating avoids problems associated withagglomeration and redispersion of particles if particles must beredispersed in the liquid feed 102 for feed to the aerosol generator106. For example, for particles originally precipitated from a liquidmedium, the liquid medium containing the suspended precipitatedparticles could be used to form the liquid feed 102 to the aerosolgenerator 106. It should be noted that the particle coater 350 could bean integral extension of the furnace 110 or could be a separate piece ofequipment.

In a further embodiment of the present invention, following preparationof the particles 112 in the furnace 110, the particles 112 may then bestructurally modified to impart desired physical properties prior toparticle collection. Referring now to FIG. 34, one embodiment of theprocess of the present invention is shown including such structuralparticle modification. The particles 112 exiting the furnace 110 go to aparticle modifier 360 where the particles are structurally modified toform modified particles 362, which are then sent to the particlecollector 114 for preparation of the particulate product 116. Theparticle modifier 360 is typically a furnace, such as an annealingfurnace, which may be integral with the furnace 110 or may be a separateheating device. Regardless, it is important that the particle modifier360 have temperature control that is independent of the furnace 110, sothat the proper conditions for particle modification may be providedseparate from conditions required of the furnace 110 to prepare theparticles 112. The particle modifier 360, therefore, typically providesa temperature controlled environment and necessary residence time toeffect the desired structural modification of the particles 112.

The structural modification that occurs in the particle modifier 360 maybe any modification to the crystalline structure or morphology of theparticles 112. For example, the particles 112 may be annealed in theparticle modifier 360 to densify the particles 112 or to recrystallizethe particles 112. Also, the particles may be annealed for a sufficienttime to permit redistribution within the particles 112 of the differentmaterial phases.

The initial morphology of composite particles made in the furnace 110,according to the present invention, could take a variety of forms,depending upon the specified materials involved and the specificprocessing conditions. Examples of some possible composite particlemorphologies, manufacturable according to the present invention areshown in FIG. 35. These morphologies could be of the particles asinitially produced in the furnace 110 or that result from structuralmodification in the particle modifier 360. Furthermore, the compositeparticles could include a mixture of the morphological attributes shownin FIG. 35.

Aerosol generation with the process of the present invention has thusfar been described with respect to the ultrasonic aerosol generator. Useof the ultrasonic generator is preferred for the process of the presentinvention because of the extremely high quality and dense aerosolgenerated. In some instances, however, the aerosol generation for theprocess of the present invention may have a different design dependingupon the specific application of the battery powders. For example, whenlarger particles are desired, such as those having an average size oflarger than about 3 μm, a spray nozzle atomizer may be preferred. Aspray nozzle atomizer also typically has a higher production rate thanultrasonic atomizers, leading to better production efficiency of thepowders. For smaller-particle applications, however, and particularlyfor those applications to produce particles smaller than about 3 μm theultrasonic generator, as described herein, is particularly preferred. Inthat regard, the ultrasonic generator of the present invention isparticularly preferred for when making particles with a weight averagesize of from about 0.1 μm to about 3 μm.

Although ultrasonic aerosol generators have been used for medicalapplications and home humidifiers, use of ultrasonic generators forspray pyrolysis particle manufacture has largely been confined tosmall-scale, experimental situations. The ultrasonic aerosol generatorof the present invention described with reference to FIGS. 2-21,however, is well suited for commercial production of high qualitypowders with a small average size and a narrow size distribution. Inthat regard, the aerosol generator produces a high quality aerosol, withheavy droplet loading and at a high rate of production. Such acombination of small droplet size, narrow size distribution, heavydroplet loading, and high production rate provide significant advantagesover existing aerosol generators that usually suffer from at least oneof inadequately narrow size distribution, undesirably low dropletloading, or unacceptably low production rate.

Through the careful and controlled design of the ultrasonic generator ofthe present invention, an aerosol may be produced typically havinggreater than about 70 weight percent (and preferably greater than about80 weight percent) of droplets in the size range of from about 1 μm toabout 10 μm, preferably in a size range of from about 1 μm to about 5 μmand more preferably from about 2 μm to about 4 μm. Also, the ultrasonicgenerator of the present invention is capable of delivering high outputrates of liquid feed in the aerosol. The rate of liquid feed, at thehigh liquid loadings previously described, is preferably greater thanabout 25 milliliters per hour per transducer, more preferably greaterthan about 37.5 milliliters per hour per transducer, even morepreferably greater than about 50 milliliters per hour per transducer andmost preferably greater than about 100 millimeters per hour pertransducer. This high level of performance is desirable for commercialoperations and is accomplished with the present invention with arelatively simple design including a single precursor bath over an arrayof ultrasonic transducers. The ultrasonic generator is made for highaerosol production rates at a high droplet loading, and with a narrowsize distribution of droplets. The generator preferably produces anaerosol at a rate of greater than about 0.5 liter per hour of droplets,more preferably greater than about 2 liters per hour of droplets, stillmore preferably greater than about 5 liters per hour of droplets, evenmore preferably greater than about 10 liters per hour of droplets andmost preferably greater than about 40 liters per hour of droplets. Forexample, when the aerosol generator has a 400 transducer design, asdescribed with reference to FIGS. 4-21, the aerosol generator is capableof producing a high quality aerosol having high droplet loading aspreviously described, at a total production rate of preferably greaterthan about 10 liters per hour of liquid feed, more preferably greaterthan about 15 liters per hour of liquid feed, even more preferablygreater than about 20 liters per hour of liquid feed and most preferablygreater than about 40 liters per hour of liquid feed.

Under most operating conditions, when using such an aerosol generator,total particulate product produced is preferably greater than about 0.5gram per hour per transducer, more preferably greater than about 0.75gram per hour per transducer, even more preferably greater than about1.0 gram per hour per transducer and most preferably greater than about2.0 grams per hour per transducer.

One significant aspect of the process of the present invention formanufacturing particulate materials is the unique flow characteristicsencountered in the furnace relative to laboratory scale systems. Themaximum Reynolds number attained for flow in the furnace 110 with thepresent invention is very high, typically in excess of 500, preferablyin excess of 1,000 and more preferably in excess of 2,000. In mostinstances, however, the maximum Reynolds number for flow in the furnacewill not exceed 10,000, and preferably will not exceed 5,000. This issignificantly different from lab-scale systems where the Reynolds numberfor flow in a reactor is typically lower than 50 and rarely exceeds 100.

The Reynolds number is a dimensionless quantity characterizing flow of afluid which, for flow through a circular cross sectional conduit isdefined as: ${Re} = \frac{vd}{\mu}$where:

-   -   =fluid density;    -   v=fluid mean velocity;    -   d=conduit inside diameter; and    -   μ=fluid viscosity.        It should be noted that the values for density, velocity and        viscosity will vary along the length of the furnace 110. The        maximum Reynolds number in the furnace 110 is typically attained        when the average stream temperature is at a maximum, because the        gas velocity is at a very high value due to gas expansion when        heated.

One problem with operating under flow conditions at a high Reynoldsnumber is that undesirable volatilization of components is much morelikely to occur than in systems having flow characteristics as found inlaboratory-scale systems. The volatilization problem occurs with thepresent invention, because the furnace is typically operated over asubstantial section of the heating zone in a constant wall heat fluxmode, due to limitations in heat transfer capability. This issignificantly different than operation of a furnace at a laboratoryscale, which typically involves operation of most of the heating zone ofthe furnace in a uniform wall temperature mode, because the heating loadis sufficiently small that the system is not heat transfer limited.

With the present invention, it is typically preferred to heat theaerosol stream in the heating zone of the furnace as quickly as possibleto the desired temperature range for particle manufacture. Because offlow characteristics in the furnace and heat transfer limitations,during rapid heating of the aerosol the wall temperature of the furnacecan significantly exceed the maximum average target temperature for thestream. This is a problem because, even though the average streamtemperature may be within the range desired, the wall temperature maybecome so hot that components in the vicinity of the wall are subjectedto temperatures high enough to undesirably volatilize the components.This volatilization near the wall of the furnace can cause formation ofsignificant quantities of ultrafine particles that are outside of thesize range desired.

Therefore, with the present invention, it is preferred that when theflow characteristics in the furnace are such that the Reynolds numberthrough any part of the furnace exceeds 500, more preferably exceeds1,000, and most preferably exceeds 2,000, the maximum wall temperaturein the furnace should be kept at a temperature that is below thetemperature at which a desired component of the final particles wouldexert a vapor pressure not exceeding about 200 millitorr, morepreferably not exceeding about 100 millitorr, and most preferably notexceeding about 50 millitorr. Furthermore, the maximum wall temperaturein the furnace should also be kept below a temperature at which anintermediate component, from which a final component is to be at leastpartially derived, should also have a vapor pressure not exceeding themagnitudes noted for components of the final product.

In addition to maintaining the furnace wall temperature below a levelthat could create volatilization problems, it is also important thatthis not be accomplished at the expense of the desired average streamtemperature. The maximum average stream temperature must be maintainedat a high enough level so that the particles will have a desired highdensity. The maximum average stream temperature should, however,generally be a temperature at which a component in the final particles,or an intermediate component from which a component in the finalparticles is at least partially derived, would exert a vapor pressurenot exceeding about 100 millitorr, preferably not exceeding about 50millitorr, and most preferably not exceeding about 25 millitorr.

So long as the maximum wall temperature and the average streamtemperature are kept below the point at which detrimental volatilizationoccurs, it is generally desirable to heat the stream as fast as possibleand to remove resulting particles from the furnace immediately after themaximum stream temperature is reached in the furnace. With the presentinvention, the average residence time in the heating zone of the furnacemay typically be maintained at shorter than about 4 seconds, preferablyshorter than about 2 seconds, more preferably shorter than about 1second, still more preferably shorter than about 0.5 second, and mostpreferably shorter than about 0.2 second.

Another significant issue with respect to operating the process of thepresent invention, which includes high aerosol flow rates, is losswithin the system of materials intended for incorporation into the finalparticulate product. Material losses in the system can be quite high ifthe system is not properly operated. If system losses are too high, theprocess would not be practical for use in the manufacture of particulateproducts of many materials. This has typically not been a majorconsideration with laboratory-scale systems.

One significant potential for loss with the process of the presentinvention is thermophoretic losses that occur when a hot aerosol streamis in the presence of a cooler surface. In that regard, the use of thequench cooler, as previously described, with the process of the presentinvention provides an efficient way to cool the particles withoutunreasonably high thermophoretic losses. There is also, however,significant potential for losses occurring near the end of the furnaceand between the furnace and the cooling unit.

It has been found that thermophoretic losses in the back end of thefurnace can be significantly controlled if the heating zone of thefurnace is operated such that the maximum stream temperature is notattained until near the end of the heating zone in the furnace, and atleast not until the last third of the heating zone. When the heatingzone includes a plurality of heating sections, the maximum averagestream temperature should ordinarily not occur until at least the lastheating section. Furthermore, the heating zone should typically extendto as close to the exit of the furnace as possible. This is counter toconventional thought which is to typically maintain the exit portion ofthe furnace at a low temperature to avoid having to seal the furnaceoutlet at a high temperature. Such cooling of the exit portion of thefurnace, however, significantly promotes thermophoretic losses.Furthermore, the potential for operating problems that could result inthermophoretic losses at the back end of the furnace are reduced withthe very short residence times in the furnace for the present invention,as discussed previously.

Typically, it would be desirable to instantaneously cool the aerosolupon exiting the furnace. This is not possible. It is possible, however,to make the residence time between the furnace outlet and the coolingunit as short as possible. Furthermore, it is desirable to insulate theaerosol conduit occurring between the furnace exit and the cooling unitentrance. Even more preferred is to insulate that conduit and, even morepreferably, to also heat that conduit so that the wall temperature ofthat conduit is at least as high as the average stream temperature ofthe aerosol stream. Furthermore, it is desirable that the cooling unitoperate in a manner such that the aerosol is quickly cooled in a mannerto prevent thermophoretic losses during cooling. The quench cooler,described previously, is very effective for cooling with low losses.Furthermore, to keep the potential for thermophoretic losses very low,it is preferred that the residence time of the aerosol stream betweenattaining the maximum stream temperature in the furnace and a point atwhich the aerosol has been cooled to an average stream temperature belowabout 200° C. is shorter than about 2 seconds, more preferably shorterthan about 1 second, and even more preferably shorter than about 0.5second and most preferably shorter than about 0.1 second. Furthermore,the total residence time from the beginning of the heating zone in thefurnace to a point at which the average stream temperature is at atemperature below about 200° C. should typically be shorter than about 5seconds, preferably shorter than about 3 seconds, more preferablyshorter than about 2 seconds, and most preferably shorter than about 1second.

Another part of the process with significant potential forthermophoretic losses is after particle cooling until the particles arefinally collected. Proper particle collection is very important toreducing losses within the system. The potential for thermophoreticlosses is significant following particle cooling because the aerosolstream is still at an elevated temperature to prevent detrimentalcondensation of water in the aerosol stream. Therefore, cooler surfacesof particle collection equipment can result in significantthermophoretic losses.

To reduce the potential for thermophoretic losses before the particlesare finally collected, it is important that the transition between thecooling unit and particle collection be as short as possible.Preferably, the output from the quench cooler is immediately sent to aparticle separator, such as a filter unit or a cyclone. In that regard,the total residence time of the aerosol between attaining the maximumaverage stream temperature in the furnace and the final collection ofthe particles is preferably shorter than about 2 seconds, morepreferably shorter than about 1 second, still more preferably shorterthan about 0.5 second and most preferably shorter than about 0.1 second.Furthermore, the residence time between the beginning of the heatingzone in the furnace and final collection of the particles is preferablyshorter than about 6 seconds, more preferably shorter than about 3seconds, even more preferably shorter than about 2 seconds, and mostpreferably shorter than about 1 second. Furthermore, the potential forthermophoretic losses may further be reduced by insulating the conduitsection between the cooling unit and the particle collector and, evenmore preferably, by also insulating around the filter, when a filter isused for particle collection. The potential for losses may be reducedeven further by heating of the conduit section between the cooling unitand the particle collection equipment, so that the internal equipmentsurfaces are at least slightly warmer than the aerosol stream averagestream temperature. Furthermore, when a filter is used for particlecollection, the filter could be heated. For example, insulation could bewrapped around a filter unit, with electric heating inside of theinsulating layer to maintain the walls of the filter unit at a desiredelevated temperature higher than the temperature of filter elements inthe filter unit, thereby reducing thermophoretic particle losses towalls of the filter unit.

Even with careful operation to reduce thermophoretic losses, some losseswill still occur. For example, some particles will inevitably be lost towails of particle collection equipment, such as the walls of a cycloneor filter housing. One way to reduce these losses, and correspondinglyincrease product yield, is to periodically wash the interior of theparticle collection equipment to remove particles adhering to the sides.In most cases, the wash fluid will be water, unless water would have adetrimental effect on one of the components of the particles. Forexample, the particle collection equipment could include parallelcollection paths. One path could be used for active particle collectionwhile the other is being washed. The wash could include an automatic ormanual flush without disconnecting the equipment. Alternatively, theequipment to be washed could be disconnected to permit access to theinterior of the equipment for a thorough wash. As an alternative tohaving parallel collection paths, the process could simply be shut downoccasionally to permit disconnection of the equipment for washing. Theremoved equipment could be replaced with a clean piece of equipment andthe process could then be resumed while the disconnected equipment isbeing washed.

For example, a cyclone or filter unit could periodically be disconnectedand particles adhering to interior walls could be removed by a waterwash. The particles could then be dried in a low temperature dryer,typically at a temperature of lower than about 50° C.

Another area for potential losses in the system, and for the occurrenceof potential operating problems, is between the outlet of the aerosolgenerator and the inlet of the furnace. Losses here are not due tothermophoresis, but rather to liquid coming out of the aerosol andimpinging and collecting on conduit and equipment surfaces. Althoughthis loss is undesirable from a material yield standpoint, the loss maybe even more detrimental to other aspects of the process. For example,water collecting on surfaces may release large droplets that can lead tolarge particles that detrimentally contaminate the particulate product.Furthermore, if accumulated liquid reaches the furnace, the liquid cancause excessive temperature gradients within the furnace tube, which cancause furnace tube failure, especially for ceramic tubes. One way toreduce the potential for undesirable liquid buildup in the system is toprovide adequate drains, as previously described. In that regard, it ispreferred that a drain be placed as close as possible to the furnaceinlet to prevent liquid accumulations from reaching the furnace. Thedrain should be placed, however, far enough in advance of the furnaceinlet such that the stream temperature is lower than about 80° C. at thedrain location.

Another way to reduce the potential for undesirable liquid buildup isfor the conduit between the aerosol generator outlet and the furnaceinlet to be of a substantially constant cross sectional area andconfiguration. Preferably, the conduit beginning with the aerosolgenerator outlet, passing through the furnace and continuing to at leastthe cooling unit inlet is of a substantially constant cross sectionalarea and geometry.

Another way to reduce the potential for undesirable buildup is to heatat least a portion, and preferably the entire length, of the conduitbetween the aerosol generator and the inlet to the furnace. For example,the conduit could be wrapped with a heating tape to maintain the insidewalls of the conduit at a temperature higher than the temperature of theaerosol. The aerosol would then tend to concentrate toward the center ofthe conduit due to thermophoresis. Fewer aerosol droplets would,therefore, be likely to impinge on conduit walls or other surfacesmaking the transition to the furnace.

Another way to reduce the potential for undesirable liquid buildup is tointroduce a dry gas into the aerosol between the aerosol generator andthe furnace. Referring now to FIG. 36, one embodiment of the process isshown for adding a dry gas 118 to the aerosol 108 before the furnace110. Addition of the dry gas 118 causes vaporization of at least a partof the moisture in the aerosol 108, and preferably substantially all ofthe moisture in the aerosol 108, to form a dried aerosol 119, which isthen introduced into the furnace 110.

The dry gas 118 will most often be dry air, although in some instancesit may be desirable to use dry nitrogen gas or some other dry gas. Ifsufficient a sufficient quantity of the dry gas 118 is used, thedroplets of the aerosol 108 are substantially completely dried tobeneficially form dried precursor particles in aerosol form forintroduction into the furnace 110, where the precursor particles arethen pyrolyzed to make a desired particulate product. Also, the use ofthe dry gas 118 typically will reduce the potential for contact betweendroplets of the aerosol and the conduit wall, especially in the criticalarea in the vicinity of the inlet to the furnace 110. In that regard, apreferred method for introducing the dry gas 118 into the aerosol 108 isfrom a radial direction into the aerosol 108. For example, equipment ofsubstantially the same design as the quench cooler, described previouslywith reference to FIGS. 29-31, could be used, with the aerosol 108flowing through the interior flow path of the apparatus and the dry gas118 being introduced through perforated wall of the perforated conduit.An alternative to using the dry gas 118 to dry the aerosol 108 would beto use a low temperature thermal preheater/dryer prior to the furnace110 to dry the aerosol 108 prior to introduction into the furnace 110.This alternative is not, however, preferred.

Still another way to reduce the potential for losses due to liquidaccumulation is to operate the process with equipment configurationssuch that the aerosol stream flows in a vertical direction from theaerosol generator to and through the furnace. For smaller-sizeparticles, those smaller than about 1.5 μm, this vertical flow should,preferably, be vertically upward. For larger-size particles, such asthose larger than about 1.5 μm, the vertical flow is preferablyvertically downward.

Furthermore, with the process of the present invention, the potentialfor system losses is significantly reduced because the total systemretention time from the outlet of the generator until collection of theparticles is typically shorter than about 10 seconds, preferably shorterthan about 7 seconds, more preferably shorter than about 5 seconds andmost preferably shorter than about 3 seconds.

For the production of fine battery particles according to the presentinvention, the liquid feed 102 includes at least one battery compoundprecursor. The precursor may be a substance in either a liquid or solidphase of the liquid feed 102. Preferably, the precursor will be ametal-containing compound, such as a salt, dissolved in a liquid solventof the liquid feed 102. The precursor may undergo one or more chemicalreactions in the furnace 110 to assist in production of the particles112.

For example, the liquid feed 102 can comprise a solution containingnitrates, chlorides, sulfates, hydroxides, or carboxylates of a metal. Apreferred component of the battery compound according to the presentinvention is lithium and a preferred precursor to lithium according tothe present invention is lithium nitrate.

The solution preferably has a precursor concentration that isunsaturated to avoid the possibility of precipitate formation in theprecursor solution. The solution preferably includes a soluble precursorto yield a concentration of from about 1 to about 50 weight percent ofthe battery compound, more preferably from about 1 to 20 weight percentof the battery compound and even more preferably from about 3 to about15 weight percent of the battery compound, such as about 5 weightpercent of the battery compound. The final particle size of theparticles 112 is also influenced by the precursor concentration.Generally, lower precursor concentrations will produce particles havinga smaller average particle size.

Preferably, the solvent is aqueous-based for ease of operation, althoughother solvents, such as toluene, may be desirable. As is disclosedabove, the pH of the aqueous-based solutions can be adjusted to alterthe solubility characteristics of the precursor in the solution.

Thus, the liquid feed 102 includes multiple precursor materials, whichmay be present together in a single phase or separately in multiplephases. For example, the liquid feed 102 may include multiple precursorsin solution in a single liquid vehicle. Alternatively, one precursormaterial could be in a solid particulate phase and a second precursormaterial could be in a liquid phase. Also, one precursor material couldbe in one liquid phase and a second precursor material could be in asecond liquid phase, such as could be the case for when the liquid feed102 comprises an emulsion.

A carrier gas 104 under controlled pressure is introduced to the aerosolgenerator to move the droplets away from the generator. The carrier gas104 may comprise any gaseous medium in which droplets produced from theliquid feed 102 may be dispersed in aerosol form. The carrier gas 104can be inert, in that the carrier gas 104 does not directly participatein the formation of the particles 112. Alternatively, the carrier gas104 may have one or more active component(s) that contribute toformation of the particles 112. For the production of fine batteryparticles 112, according to the present invention, the preferred carriergas is air, which advantageously provides oxygen during formation of theparticles.

Many battery materials can be difficult to produce using conventionalmethods such that the powders have the desirable physical andelectrochemical characteristics. Many such compounds can be difficult toproduce even using a standard spray pyrolysis technique.

These compounds can advantageously be produced according to the presentinvention using a process referred to as spray-conversion.Spray-conversion is a process wherein a spray pyrolysis technique, as isdescribed above, is used to produce an intermediate particulate productthat is capable of being subsequently converted to the a particulatebattery compound having the desirable properties. The intermediateproduct advantageously has many of the desirable morphologicalproperties discussed hereinbelow, such as a small particle size and anarrow particle size distribution.

As is discussed above, precursor materials including water-solubleprecursors, such as nitrate salts, are placed into solution, atomizedand are converted at a relatively low temperature, such as less thanabout 1000° C., to intermediate particles comprised of low crystallinityoxide phase(s). The intermediate particles have a small size and,preferably, a narrow particle size distribution, as is described in moredetail below. The intermediate particles are then converted by furthertreatment, such as by heat treating at an elevated temperature, to forman active battery compound having high crystallinity and goodelectrochemical characteristics. The resulting powder advantageouslydoes not require any further milling to reduce particle size or reduceagglomerates since the intermediate particles have the desired size andagglomeration is avoided during the subsequent heat treatment. Theresulting end product is a highly crystalline powder having thedesirable properties. The average particle size and morphologicalcharacteristics are determined by the characteristics of theintermediate product.

Thus, the precursors can be spray-converted at a temperature of, forexample, less than about 1000° C. to form a homogeneous admixture of oneor more oxides having low crystallinity. The intermediate particles canthen be heat treated at a temperature of, for example, 800° C. to 1700°C., to form the substantially phase pure battery compounds.

Depending on the reaction temperature, the residence time in the heatingzone can vary. It is preferred however that the residence time betypically no more than about 10 seconds, such as from about 1 to 2seconds.

To form substantially uniform coatings on the surface of the activebattery particles such as those discussed above, a reactive gascomposition can be contacted with the particles at an elevatedtemperature after the particles have been formed. For example, thereactive gas can be introduced into the heated reaction zone at thedistal end so that the desired compound deposits on the surface of theparticle.

More specifically, the droplets can enter the heated reaction zone at afirst end such that the droplets move through the heating zone and formthe particles. At the opposite end of the heating zone, a reactive gascomposition can be introduced such that the reactive gas compositioncontacts the particles at an elevated temperature. Alternatively, thereactive gas composition can be contacted with the heated particles in aseparate heating zone located downstream from the heated reaction zone.

Coatings can be generated on the particle surface by a number ofdifferent mechanisms. One or more precursors can vaporize and fuse tothe hot particle surface and thermally react resulting in the formationof a thin-film coating by chemical vapor deposition (CVD). Preferredcoatings deposited by CVD include metal oxides and elemental metals.Further, the coating can be formed by physical vapor deposition (PVD)wherein a coating material physically deposits on the surface of theparticles. Preferred coatings deposited by PVD include organic materialsand elemental metals. Alternatively, the gaseous precursor can react inthe gas phase forming small particles, for example less than about 5nanometers in size, which then diffuse to the larger particle surfaceand sinter onto the surface, thus forming a coating. This method isreferred to as gas-to-particle conversion (GPC). Whether such coatingreactions occur by CVD, PVD or GPC is dependent on the reactorconditions, such as temperature, precursor partial pressure, waterpartial pressure and the concentration of particles in the gas stream.Another possible surface coating method is surface conversion of thesurface of the particles by reaction with a vapor phase reactant toconvert the surface of the particles to a different material than thatoriginally contained in the particles.

In addition, a volatile coating material such as PbO, MoO₃ or V₂O₅ canbe introduced into the reactor such that the coating deposits on theparticles by condensation. Further, the particles can be coated usingother techniques. For example, soluble precursors to both the batterypowder and the coating can be used in the precursor solution wherein thecoating precursor is involatile, (e.g. Al(NO₃)₃) or volatile (e.g.Sn(OAc)₄ where OAc is acetate). In another embodiment, a colloidalprecursor and a soluble metal precursor can be used to form aparticulate colloidal coating on the particle. It will be appreciatedthat multiple coatings can be deposited on the surface of the particlesif such multiple coatings are desirable.

The coatings are preferably as thin as possible while maintainingconformity about particle such that the battery material is notsubstantially exposed. For example, coatings can have an averagethickness of no greater than about 200 nanometers, preferably no greaterthan about 100 nanometers, and more preferably no greater than about 50nanometers. For most applications, the coating should have an averagethickness of at least about 5 nanometers.

The structural modification that occurs in the particle modifier 360 maybe any modification to the crystalline structure or morphology of theparticles 112. For example, the particles 112 may be annealed in theparticle modifier 360 to densify the particles 112 or to recrystallizethe particles 112. Also, the particles may be annealed for a sufficienttime to redistribute the different material phases within the particles112.

The present invention is directed to fine battery powder batches whereinthe particles constituting the powder batch preferably have a sphericalmorphology, a small average particle size and a narrow particle sizedistribution. The powders according to the present invention are usefulfor a number of battery applications including use in both primary andsecondary batteries. Among the batteries to which the powders areapplicable are primary batteries based on Zn/MnO₂ and secondarybatteries based on nickel-cadmium (Ni/Cd), nickel metal hydrides(Ni/MH_(y)), lithium/manganese dioxide (Li/MnO₂) and lithium ion batterymaterials including lithium manganese oxide (LiMn₂O₄ spinel), lithiumcobalt oxide (LiCoO₂) and lithium nickel oxide (LiNiO₂).

The fine battery powder batches according to the present invention areparticularly applicable to the production of the foregoing lithium ioncompounds. While LiCoO₂, LiNiO₂ and LiMn₂O₄ are preferred, other metalscan be substituted for Co, Ni and Mn and the amount of Li can be variedto tailor the properties for specific applications. Exemplary compoundsof this type include Li_(y)CO_(1-x)Ni_(x)O₂, Li_(y)Mn_(2-x)Ni_(x)O₄ andLi_(y)Mn_(2-x)Co_(x)O₄, where y can vary from 0 to 2.

The fine battery powders according to the present invention includeparticles having a small average particle size. The preferred averagesize of the particles will vary according to the particular applicationof the powder and the present invention advantageously provides theability to carefully control the average particle size. Generally, theweight average particle size of the battery particles is at least about0.05 μm and preferably is at least about 0.1 μm, such as at least about0.3 μm. Further, the average particle size is preferably not greaterthan about 20 μm. For most applications, the weight average particlesize is more preferably not greater than about 10 μm and even morepreferably is not greater than about 5 μm. A particularly preferredaverage particle size is from about 1 μm to about 5 μm.

It is also possible according to the present invention to provide a finebattery powder batch having a bimodal particle size distribution. Thatis, the powder batch can include battery particles having two distinctand different average particle sizes. A bimodal particle sizedistribution can enhance the packing efficiency of the powder which isimportant for use as a battery electrode.

According to one preferred embodiment of the present invention, thepowder batch of fine battery particles has a narrow particle sizedistribution, such that the majority of particles are about the samesize. A narrow size distribution is particularly advantageous forapplications wherein the powder is applied in a flowable medium, such asa paste. Preferably, at least about 80 weight percent and morepreferably at least about 90 weight percent of the particles are notlarger than twice the weight average particle size. Thus, when theaverage particle size is about 2 μm, it is preferred that at least about80 weight percent of the particles are not larger than 4 μm and it ismore preferred that at least about 90 weight percent of the particlesare not larger than 4 μm. Further, it is preferred that at least about80 weight percent and more preferably at least about 90 weight percentof the particles are not larger than about 1.5 times the weight averageparticle size. Thus, when the average particle size is about 2 μm, it ispreferred that at least about 80 weight percent of the particles are notlarger than 3 μm and it is more preferred that at least about 90 weightpercent of the particles are not larger than 3 μm.

Powders produced by the processes described herein, particularly thosethat have experienced a post treatment step, generally exit as softagglomerates of primary spherical particles. It is well known to thosein the art that micrometer-sized particles often form soft agglomeratesas a result of their relatively high surface energy, as compared tolarger particles. It is also known to those skilled in the art that suchsoft agglomerates may be dispersed easily by treatments such as exposureto ultrasound in a liquid medium or sieving. The average particle sizeand particle size distributions described herein are measured by mixingsamples of the powders in a medium such as water with a surfactant and ashort exposure to ultrasound through either an ultrasonic bath or horn.The ultrasonic treatment supplies sufficient energy to disperse the softagglomerates into primary spherical particles. The primary particle sizeand size distribution is then measured by light scattering in aMicrotrac instrument. This provides a good measure of the usefuldispersion characteristics of the powder because this simulates thedispersion of the particles in a liquid medium such as a paste or slurrythat is used to deposit the particles in a device, such as a battery.Thus, the references to particle size herein refer to the primaryparticle size, such as after lightly dispersing the soft agglomerates ofparticles.

Further, it is advantageous according to the present invention that theforegoing description of the average size and size distribution of theparticles also applies to the intermediate precursor particles that areproduced during the pyrolization step. That is, the size and sizedistribution of the particles changes very little, if at all, during theheat treatment step after pyrolization. The morphological properties ofthe final battery powder are substantially controlled by the propertiesof the intermediate precursor particles.

The fine battery particles of the present invention comprise of a numberof crystallites. A battery material having a high crystallinity, i.e.large average crystallite size, can enhance the electrical properties ofbatteries formed from the fine battery powder.

Thus, according to one embodiment of the present invention, it ispreferred that the average crystallite size is such that the particlesinclude relatively large crystallites. According to this embodiment, theaverage crystallite size is preferably at least about 20 nanometers,more preferably is at least about 30 nanometers, even more preferably isat least about 40 nanometers, and most preferably is at least about 50nanometers. In one embodiment, the average crystallite size is at leastabout 100 nanometers. Fine battery powders having such highcrystallinity can advantageously have enhanced electrical properties ascompared to fine battery powders having lower crystallinity, i.e., asmaller average crystallite size. The method of the present inventionadvantageously permits control over the crystallinity of the material bycontrolling the reaction temperature and/or residence time.

The fine battery particles produced according to the present inventionalso have a high degree of purity and it is preferred that the particlesinclude not greater than about 0.1 atomic percent impurities and morepreferably not greater than about 0.01 atomic percent impurities. Sinceno milling of the particles is required to achieve small averageparticle sizes, there are substantially no undesired impurities such asalumina, zirconia or high carbon steel in the powder batch.

For many applications it is desirable to have battery particles producedwith a well controlled high porosity. Such particles can advantageouslyalso be produced according to the present invention. Battery powdershaving a high degree of open (accessible) porosity can advantageouslyform a battery having a high discharge rate.

The fine battery particles according to a preferred embodiment of thepresent invention are also substantially spherical in shape. That is,the particles are not jagged or irregular in shape. Spherical particlesare particularly advantageous because they are able to disperse morereadily in a paste or slurry and impart advantageous flowcharacteristics to the paste of slurry compositions.

As is discussed above, it is desirable to provide fine battery powdershaving an increased surface area and a high degree of open (accessible)porosity.

In addition, the powder batches of fine battery particles according tothe present invention are substantially unagglomerated, that is, theyinclude substantially no hard agglomerates of particles. Hardagglomerates are physically coalesced lumps of two or more particlesthat behave as one large particle. Hard agglomerates are disadvantageousin most applications of the battery powders. It is preferred that nomore than about 1.0 weight percent of the fine battery particles in thepowder batch of the present invention are in the form of hardagglomerates. More preferably, no more than about 0.5 weight percent ofthe particles are in the form of hard agglomerates. In the event thatthe powder does include hard agglomerates, such hard agglomerates can beremoved by, for example, jet-milling the powder.

The fine battery powder batches according to the present invention areuseful in a number of applications and can be used to fabricate a numberof novel devices and intermediate products. Such devices andintermediate products are included within the scope of the presentinvention.

The fine battery powders of the present invention are particularlyuseful in electrocatalytic devices, such as batteries. One suchapplication of the fine battery powders according to the presentinvention is in the field of batteries. For example, the fine batterypowders are particularly advantageous for use in the electrodes of alithium ion battery.

The battery powders are typically deposited onto device surfaces orsubstrates by a number of different deposition methods which involve thedirect deposition of the dry powder such as dusting, electrophotographicor electrostatic precipitation, while other deposition methods involveliquid vehicles such as ink jet printing, liquid delivery from asyringe, micro-pens, toner, slurry deposition, paste-based methods andelectrophoresis. In all these deposition methods, the powders describedin the present invention show a number of distinct advantages over thepowders produced by other methods. For example, small, spherical, narrowsize distribution particles are more easily dispersed in liquidvehicles, they remain dispersed for a longer period and allow printingof smoother and finer features compared to powder made by alternativemethods.

One way of applying such powders to a substrate is through the use of athick-film paste. In the thick film process, a viscous paste thatincludes a functional particulate phase (e.g. a fine battery powder) isscreen printed onto a substrate. More particularly, a porous screenfabricated from stainless steel, polyester, nylon or similar inertmaterial is stretched and attached to a rigid frame. A predeterminedpattern is formed on the screen corresponding to the pattern to beprinted. For example, a UV sensitive emulsion can be applied to thescreen and exposed through a positive or negative image of the designpattern. The screen is then developed to remove portions of the emulsionin the pattern regions.

The screen is then affixed to a screen printing device and the thickfilm paste is deposited on top of the screen. The substrate to beprinted is then positioned beneath the screen and the paste is forcedthrough the screen and onto the substrate by a squeegee that traversesthe screen. Thus, a pattern of traces and/or pads of the paste materialis transferred to the substrate. The substrate with the paste applied ina predetermined pattern is then subjected to a drying and firingtreatment to solidify and adhere the paste to the substrate.

Thick film pastes have a complex chemistry and generally include afunctional phase, a binder phase and an organic vehicle phase. Thefunctional phase include the fine battery powders of the presentinvention which provide conductivity. The binder phase can be, forexample, a mixture of metal oxide or glass frit powders. PbO basedglasses are commonly used as binders. The function of the binder phaseis to control the sintering of the film and assist the adhesion of thefunctional phase to the substrate and/or assist in the sintering of thefunctional phase. Reactive compounds can also be included in the pasteto promote adherence of the functional phase to the substrate.

Thick film pastes also include an organic vehicle phase that is amixture of solvents, polymers, resins and other organics whose mainfunction is to provide the appropriate rheology (flow properties) to thepaste. The liquid solvent assists in mixing of the components into ahomogenous paste and substantially evaporates upon application of thepaste to the substrate. Usually the solvent is a volatile liquid such asmethanol, ethanol, terpineol, butyl carbitol, butyl carbitol acetate,aliphatic alcohols, esters, acetone and the like. The other organicvehicle components can include thickeners (sometimes referred to asorganic binders), stabilizing agents, surfactants, wetting agents andthe like. Thickeners provide sufficient viscosity to the paste and alsoacts as a binding agent in the unfired state. Examples of thickenersinclude ethyl cellulose, polyvinyl acetates, resins such as acrylicresin, cellulose resin, polyester, polyamide and the like. Thestabilizing agents reduce oxidation and degradation, stabilize theviscosity or buffer the pH of the paste. For example, triethanolamine isa common stabilizer. Wetting agents and surfactants are well known inthe thick film paste art and can include triethanolamine and phosphateesters.

The different components of the thick film paste are mixed in thedesired proportions in order to produce a substantially homogenous blendwherein the functional phase is well dispersed throughout the paste.Typically, the thick film paste will include from about 5 to about 95weight percent such as from about 60 to 85 weight percent, of thefunctional phase, including the fine battery powders of the presentinvention.

Examples of thick film pastes are disclosed in U.S. Pat. Nos. 4,172,733;3,803,708; 4,140,817; and 3,816,097 all of which are incorporated hereinby reference in their entirety.

Some applications of thick film pastes require higher tolerances thancan be achieved using standard thick-film technology, as is describedabove. As a result, some thick film pastes have photo-imaging capabilityto enable the formation of lines and traces with decreased width andpitch. In this type of process, a photoactive thick film paste isapplied to a substrate substantially as is described above. The pastecan include, for example, a liquid vehicle such as polyvinyl alcohol,that is not cross-linked. The paste is then dried and exposed toultraviolet light through a photomask to polymerize the exposed portionsof paste and the paste is developed to remove unwanted portions of thepaste. This technology permits higher density lines and features to beformed. The combination of the foregoing technology with the batterypowders of the present invention permits the fabrication of devices withhigher resolution and tolerances as compared to conventionaltechnologies using conventional powders.

In addition, a laser can be used instead of ultraviolet light through amask. The laser can be scanned over the surface in a pattern therebyreplacing the need for a mask. The laser light is of sufficiently lowintensity that it does not heating the glass or polymer above itssoftening point. The unirradiated regions of the paste can be removedleaving a pattern. Likewise, conventional paste technology utilizesheating of a substrate to remove the vehicle from a paste and to fuseparticles together or modify them in some other way. A laser can be usedto locally heat the paste layer and scanned over the paste layer therebyforming a pattern. The laser heating is confined to the paste layer anddrives out the paste vehicle and heats the powder in the paste withoutappreciably heating the substrate. This allows heating of particles,delivered using pastes, without damaging a glass or even polymericsubstrate.

Other deposition methods for the battery powders can also be used. Forexample, a slurry method can be used to deposit the powder. The powderis typically dispersed in an aqueous slurry including reagents such aspotassium silicate and polyvinyl alcohol, which aids in the adhesion ofthe powder to the surface. For example, the slurry can be poured ontothe substrate and left to settle to the surface. After the powder hassedimented onto the substrate the supernatant liquid is decanted off andthe powder layer is left to dry.

Battery particles can also be deposited electrophoretically orelectrostatically. The particles are charged and are brought intocontact with the substrate surface having localized portions of oppositecharge. The layer is typically lacquered to adhere the particles to thesubstrate. Shadow masks can be used to produce the desired pattern onthe substrate surface.

Ink-jet printing is another method for depositing the powders in apredetermined pattern. The powder is dispersed in a liquid medium anddispensed onto a substrate using an ink jet printing head that iscomputer controlled to produce a pattern. The powders of the presentinvention having a small size, narrow size distribution and sphericalmorphology can be printed into a pattern having a high density and highresolution. Other deposition methods utilizing a battery powderdispersed in a liquid medium include micro-pen or syringe deposition,wherein the powders are dispersed and applied to a substrate using a penor syringe and are then allowed to dry.

Patterns can also be formed by using an ink jet or micropen (smallsyringe) to dispense sticky material onto a surface in a pattern. Powderis then transferred to the sticky regions. This transfer can be done isseveral ways. A sheet covered with powder can be applied to the surfacewith the sticky pattern. The powder sticks to the sticky pattern anddoes not stick to the rest of the surface. A nozzle can be used totransfer powder directly to the sticky regions.

Many methods for directly depositing materials onto surfaces requireheating of the particles once deposited to sinter them together anddensify the layer. The densification can be assisted by including amolecular precursor to a material in the liquid containing theparticles. The particle/molecular precursor mixture can be directlywritten onto the surface using ink jet, micro-pen, and other liquiddispensing methods. This can be followed by heating in a furnace orheating using a localized energy source such as a laser. The heatingconverts the molecular precursor into the functional material containedin the particles thereby filling in the space between the particles withfunctional material.

Thus, the battery powders produced according to the present inventionresult in smoother powder layers when deposited by such liquid or drypowder based deposition methods. Smoother powder layers are the resultof the smaller average particle size, spherical particle morphology andnarrower particle size distribution compared to powders produced byother methods.

EXAMPLES

The following example demonstrates the preparation of fine batteryparticles according to the present invention.

1.08 grams of Mn(NO₃)₂₆H₂O (3.76×10⁻³ moles Mn) and 0.0494 grams LiOH(2.06×10⁻³ moles Li) were added to 15 ml water. Several drops ofconcentrated HNO₃ was then added and the solution was stirred todissolve the LiOH. The solution was atomized with an ultrasonictransducer and the aerosol droplets were carried in 3 liters per minuteof air through a virtual impactor to remove droplets having a sizegreater than about 10 μm. The droplets were then passed through a heatedtube furnace at a temperature of 675° C.

The resulting particles had a composition of Li_(1.1)Mn₂O₄ and anaverage particle size of about 1.1 μm with a narrow size distribution.

1-21. (canceled)
 22. A battery comprising at least one electrocatalyticlayer, wherein said electrocatalytic layer comprises fine batteryparticles having an average particle size of not greater than about 20μm and wherein said particles have a substantially spherical morphologyand said particles have a particle size distribution wherein at leastabout 80 weight percent of said particles are not larger than twice saidaverage particle size.
 23. An electrocatalytic device as recited inclaim 22, wherein said average particle size is at least about 0.3 μm.24. An electrocatalytic device as recited in claim 22, wherein saidaverage particle size is not greater than about 10 μm.
 25. Anelectrocatalytic device as recited in claim 22, wherein said battery isa lithium-ion battery. 26-31. (canceled)